The invention is generally related to the field of semiconductor device fabrication and more specifically to a method for fabricating inductors and transformers on integrated circuits
As more circuit components are being integrated on-chip there is an increasing need for integrated circuit inductors. Inductors in integrated circuits have a number of important uses in providing on-chip filtering and voltage conversion. Currently, the majority of inductors used are discrete off-chip devices that require connection to the integrated circuit (IC). The leads used for the connection adds series resistance and capacitance to the overall circuit and therefore affect the performance of the circuit. In addition, there is an additional cost associated with these discrete external inductors.
With the current trends towards system-on-a-chip integrated circuits, it is often the case that a number of different supply voltages are required on the integrated circuit. Typically, a single voltage is supplied to the IC and the remaining required voltages are obtained through voltage conversion. On-chip voltage conversion usually requires an IC transformer and filtering. This filtering is performed using capacitors and inductors. IC transformer fabrication requires efficient coupling of inductive coils and relatively large values of inductance.
Currently, IC inductors are typically fabricated as a coil in a single level of metal or using a system of multiple metal levels along with vias connecting the metal levels. Here, the core of the inductor will be the interlevel dielectric material which in most cases will be silicon dioxide. The fabrication of integrated circuit inductors with large inductance values having SiO2 as the core is made difficult due to the low relative permeability of SiO2 and the presence of traps and other defects in the SiO2 layer. If a large number of turns are used to increase the inductance, the silicon surface area required becomes prohibitively large.
Using current fabrication methods, large value inductors take up a large amount of silicon surface area making their use in current IC technology impractical.
The instant invention describes a method for fabricating a miniaturized integrated circuit inductor and transformer.
An embodiment of the instant invention is a method of forming an inductor in a semiconductor substrate with an upper surface, said method comprising the steps of: forming a magnetic structure on said semiconductor substrate; and forming a metal structure on said upper surface of said semiconductor substrate such that a magnetic flux is induced in said magnetic film. Another embodiment of the instant invention is a method of forming an inductor in a semiconductor substrate with a upper surface, said method comprising the steps of: forming a first magnetic structure on said semiconductor substrate; forming a first insulating layer on said first magnetic film; forming a second magnetic structure on said first insulating layer; forming a metal structure on said second first insulating layer such that said metal film induces a magnetic flux in said second magnetic film; forming a second insulating layer with an upper surface on said first insulating layer wherein said second insulating layer encases said second magnetic film and said metal film; and forming a third magnetic film on said second insulating layer.
Another embodiment of the instant invention is an integrated circuit transformer in a semiconductor substrate comprising: a first metal film with a first pattern; a continuous magnetic layer above said first metal film; a second metal film above said magnetic film with a second pattern; a plurality of electrically conducting contacts between said first metal film and said second metal film wherein said first metal film, said second metal film, and said electrically conducting contacts form two adjacent coils with each coil having at least one turn around said magnetic film.